Electricity cost calculator for an appliance
Enter the appliance's power in watts, how long it runs and the kWh price on your bill. A 100 W device on 4 hours a day uses 146 kWh a year.
- Checked on thousands of cases
- Updated November 6, 2026
The one on your bill
Cost per year
Energy : 146 kWh
| Energy | Cost | |
|---|---|---|
| Per day | 0.4 kWh | 0.08 |
| Per month | 12 kWh | 2.43 |
| Per year | 146 kWh | 29.20 |
= 1 kWh · Per month
Quick challenge
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How it works
Formula: kWh = W × hours ÷ 1,000; cost = kWh × price per kWh
A device of P watts running for t hours uses P × t ÷ 1,000 kilowatt-hours (kWh). Multiply by the price per kWh of your plan. A month is counted as one twelfth of a 365-day year. The power is on the appliance's label or in its manual; it is often a maximum, and many appliances use less on average (a fridge does not run all the time). The price of a kWh depends on the country, the supplier and sometimes the time of day: no rate is built in, enter your own.
Yearly energy use by power and daily use
| Power | Per hour of use | Per year at 1 h/day | Per year at 4 h/day | Per year at 24 h/day |
|---|---|---|---|---|
| 5 W | 0.005 kWh | 1.8 kWh | 7.3 kWh | 43.8 kWh |
| 10 W | 0.01 kWh | 3.7 kWh | 14.6 kWh | 87.6 kWh |
| 60 W | 0.06 kWh | 21.9 kWh | 87.6 kWh | 525.6 kWh |
| 100 W | 0.1 kWh | 36.5 kWh | 146 kWh | 876 kWh |
| 500 W | 0.5 kWh | 182.5 kWh | 730 kWh | 4,380 kWh |
| 1,000 W | 1 kWh | 365 kWh | 1,460 kWh | 8,760 kWh |
| 2,000 W | 2 kWh | 730 kWh | 2,920 kWh | 17,520 kWh |
Frequently asked questions
How do I work out an appliance's kWh?
Multiply the power in watts by the hours of use, then divide by 1,000: a 1,500 W heater on for 3 hours uses 1,500 × 3 ÷ 1,000 = 4.5 kWh.
How much does standby use?
A 5 W standby, 24 hours a day, adds up to 5 × 24 × 365 ÷ 1,000 = 43.8 kWh a year. Multiply by your kWh price to get the cost.
Where do I find my price per kWh?
On your electricity bill or plan. If your rate changes with the time of day, use the price of the hours when the appliance runs.